In recent years, with the rapid spread of information-related devices and communication devices such as personal computers, camcorders and cellular phones, it has become important to develop a battery for use as a power source for such devices. In the automobile industry, the development of high-power and high-capacity batteries for electric vehicles and hybrid vehicles has been promoted. Among various kinds of batteries, rechargeable lithium batteries have attracted attention due to their high energy density and high power.
Especially, rechargeable lithium-air batteries have attracted attention as a rechargeable lithium battery for electric vehicles and hybrid vehicles, which is required to have high energy density. Rechargeable lithium-air batteries use oxygen in the air as a cathode active material. Therefore, compared to conventional lithium rechargeable batteries containing a transition metal oxide (e.g., lithium cobaltate) as a cathode active material, rechargeable lithium-air batteries are able to have larger capacity.
In metal-air batteries, the cathode active material, oxygen, is not contained within the battery. Instead, this material is provided by the surrounding atmosphere. Naturally, such a system allows in principle a very high specific energy (energy provided by the battery per unit weight, typically given in Wh/kg in this technical field). In such batteries, oxygen may be partially reduced to peroxide, or fully reduced to hydroxide or oxide depending on the catalyst, electrolyte, availability of oxygen etc. When the negative electrode (anode) is lithium (Li), lithium peroxide (Li2O2) or lithium oxide (Li2O) may be formed.
A metal-air battery may be schematically represented in FIG. 1. It contains mainly the following parts:                metal anode (preferentially Li),        non-aqueous electrolyte,        air cathode (preferentially O2 cathode) most commonly and usually preferably based on carbon (but other cathode materials are known in this context), binder and sometimes catalyst.        
The ideal reactions during the use of such a battery should be as follows:
Upon discharge:
At anode: Li→Li++e−
At air cathode: 2 Li++x/2 O2+2e−→Li2Ox 
Upon charge:
At anode: Li++e−→Li
At air cathode: Li2Ox→2 Li++x/2 O2+2e−
In the reaction which occurs in the air cathode upon discharge, the lithium ion (Li+) is dissolved from the anode by electrochemical oxidation and transferred to the air cathode through an electrolyte. The oxygen (O2) is supplied to the air cathode.
Nevertheless, during electrochemical processes of the battery, it can happen that the O2 or O2-derived species react with the solvent molecules of the electrolyte, which may lead to the formation of side reaction products such as Li2CO3, Li formate, Li acetate etc. These products are not desirable in the battery and are believed to reduce the metal-air battery performance.
These side-reactions may lead to poor re-chargeability of the system and poor capacity retention. These general problems may be illustrated schematically as shown in FIGS. 2, 3 and 4.
The problems shown schematically in FIGS. 2, 3 and 4 may be summarized as follows:                Problem 1: Low initial capacity. This is a problem for both primary and secondary (rechargeable) metal-air non-aqueous batteries.        Problem 2: Low efficiency of system, characterized by a large voltage gap between charge and discharge voltages. This is only an issue for secondary metal-air non-aqueous batteries subjected to charging and discharging cycles.        Problem 3: Poor capacity retention, which leads to bad cyclability of the system and a low number of cycles because the capacity drops rapidly. This also is only an issue for secondary metal-air non-aqueous batteries.        Problem 4: The reaction process is slow and charge/discharge performances at high current are lower.        
In the case of a primary metal-air battery, only problems 1 and 4 are relevant.
Concerning the air cathode, in a conventional lithium-air battery, the air cathode often includes a metal grid (made from nickel, aluminium, stainless steel, or titanium for example) as an air cathode current collector, upon which an air cathode material is supported, the air cathode material comprising a conductive material such as particulate carbon. In an alternative embodiment described in EP 2 278 655 A1, carbon paper is used as an air cathode current collector. However, at higher currents (100 μA for example), the battery capacity decreases strongly and the hysteresis increases strongly (due to a combination of a lower discharge potential and a higher charge potential). Problems 1, 2, and 4 of those set out above thus remain to be solved.
In WO 00/16418, a lithium ion battery, which is a closed battery system, is disclosed which contains at least two carbon foam electrodes. Lithium air batteries containing carbon foam-based electrodes are not taught in this reference, and no means for modifying carbon foam substrates are disclosed.